[PATCH v3 2/3] spi: microchip-core-qspi: don't attempt to transmit during emulated read-only dual/quad operations

[Conor Dooley]

From: Conor Dooley <conor.dooley at microchip.com>

The core will deal with reads by creating clock cycles itself, there's
no need to generate clock cycles by transmitting garbage data at the
driver level. Further, transmitting garbage data just bricks the transfer
since QSPI doesn't have a dedicated master-out line like MOSI in regular
SPI. I'm not entirely sure if the transfer is bricked because of the
garbage data being transmitted on the bus or because the core loses
track of whether it is supposed to be sending or receiving data.

Fixes: 8f9cf02c88528 ("spi: microchip-core-qspi: Add regular transfers")
CC: stable at vger.kernel.org
Signed-off-by: Conor Dooley <conor.dooley at microchip.com>
---
 drivers/spi/spi-microchip-core-qspi.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-microchip-core-qspi.c b/drivers/spi/spi-microchip-core-qspi.c
index ffa0f33a0ae09..70215a407b5a3 100644
--- a/drivers/spi/spi-microchip-core-qspi.c
+++ b/drivers/spi/spi-microchip-core-qspi.c
@@ -690,18 +690,28 @@ static int mchp_coreqspi_transfer_one(struct spi_controller *ctlr, struct spi_de
 				      struct spi_transfer *t)
 {
 	struct mchp_coreqspi *qspi = spi_controller_get_devdata(ctlr);
+	bool dual_quad = false;
 
 	qspi->tx_len = t->len;
 
+	if (t->tx_nbits == SPI_NBITS_QUAD || t->rx_nbits == SPI_NBITS_QUAD ||
+			t->tx_nbits == SPI_NBITS_DUAL ||
+			t->rx_nbits == SPI_NBITS_DUAL)
+		dual_quad = true;
+
 	if (t->tx_buf)
 		qspi->txbuf = (u8 *)t->tx_buf;
 
 	if (!t->rx_buf) {
 		mchp_coreqspi_write_op(qspi);
-	} else {
+	} else if (!dual_quad) {
 		qspi->rxbuf = (u8 *)t->rx_buf;
 		qspi->rx_len = t->len;
 		mchp_coreqspi_write_read_op(qspi);
+	} else {
+		qspi->rxbuf = (u8 *)t->rx_buf;
+		qspi->rx_len = t->len;
+		mchp_coreqspi_read_op(qspi);
 	}
 
 	return 0;
-- 
2.53.0